A study of group B streptococcus in Brisbane : the epidemiology, detection by PCR assay and serovar prevalence

Taylor, Karen Leigh (2006) A study of group B streptococcus in Brisbane : the epidemiology, detection by PCR assay and serovar prevalence. Masters by Research thesis, Queensland University of Technology.


The neonate is still at risk of acquiring Group B Streptococcus (GBS) infection upon delivery even with the implementation of early onset GBS neonatal disease preventative protocols. GBS was reported as the most prevalent organism causing neonatal morbidity and mortality in the USA and Australia in the 1990s. GBS is also known to cause disease in children, women, the immunocompromised adult and the elderly, but it is the preterm neonates who are at greatest risk of GBS neonatal disease.

The aim of this study was to determine the prevalence of lower genital tract (LGT) colonisation with GBS in Brisbane women of child bearing age. We also aimed: (i) to compare the GBS LGT prevalence rate of Indigenous and non Indigenous women; (ii) to determine whether previously reported risk factors for LGT colonisation with GBS were also risk factors associated with GBS colonisation of women in this study; (iii) to further develop and optimise a rapid PCR assay that could detect maternal LGT GBS colonisation; and (iv) to serotype the GBS strains that were isolated from pregnant and non pregnant women who participated in this study.

This study recruited 374 women of childbearing age attending public medical providers and found an overall GBS prevalence of 98/374 (26.2%) for these Brisbane women, a rate higher than previously reported in Australia. When the GBS prevalence for pregnant women (25.6%) was compared to non pregnant women (27.2%) they were similar. We also compared the GBS LGT colonisation rate of women attending different medical providers. The GBS LGT prevalence rate for pregnant women attending the Mater was 36/118 (30.5%), whilst those women attending the Redlands Hospital antenatal clinic had a LGT GBS prevalence rate of only 7/53 (13.2%). By comparison, the LGT GBS prevalence rate for non pregnant women attending Biala Sexual Health clinic was 21/69 (30.4%) and 34/127 (26.8%) of women attending the Brisbane Family Planning Queensland were also GBS positive. The seven women recruited from Inala community centre tested negative for GBS LGT colonisation. The LGT GBS prevalence of Australian Aboriginal women was 5/22 (22.7%), a rate which was not significantly different from non-Aboriginal women 78/288 (27.1%).

Established early onset GBS neonatal disease preventative policies have been recently revised. The CDC now recommends that all pregnant women are screened for LGT GBS colonisation during late gestation, and that any GBS isolates be tested for resistance to antibiotics if the GBS positive women have an allergy to penicillin. Queensland's Department of Health recommend that Queensland medical agencies implement a non screening based preventative protocol, where clinicians monitor: women prior to labour for reported risk factors associated with maternal GBS colonisation: women in labour for 'obstetric risk factors'.

A number of risk factors have previously been reported in association with GBS LGT colonisation. However, in this current study we found that only one risk factor was significantly associated with current GBS: previous reported LGT GBS colonisation was significantly associated with maternal LGT GBS colonisation reported in this study. Women who previously tested positive for GBS were significantly more likely to be GBS positive in subsequent tests (OR 4.7; 95%CI, 1.8-12.5) compared to women with no previous history of GBS colonisation.

An assessment of adverse pregnancy outcomes, preterm deliveries, and GBS colonisation data was made. It was established that 30 women had previously given birth to one or more preterm neonates and of these 30 women, nine (30%) of them tested positive for GBS in this current study. Of the 71 women who had given birth to neonates and who had suffered an adverse pregnancy outcome 25.3% also tested positive for GBS in this current study. GBS was identified in up to 30% of all mothers who had delivered their neonate preterm, 27.4% of women who had previously suffered miscarriages and 16.7% of women who had previously had stillbirths.

In this study we found that Australian Aboriginal women also had a greater risk of delivering neonates who suffered from an adverse pregnancy outcome in comparison to all other women. Twenty one of the 22 Aboriginal women had previously been pregnant at least once, and nine (42.9%) of these women had at least one prior adverse pregnancy outcome while seven (33.3%) of these women had previously delivered at least one neonate preterm. Of the 21 Aboriginal women who had a previous pregnancy more than half the total number of Aboriginal women (11/21) had either delivered one or more neonates preterm or had suffered from one or more adverse pregnancy outcomes. When the incidence of adverse pregnancy outcomes was compared for Aboriginal and all other women the results were surprising. Overall, this study found 216 women including Aboriginal women had previously been pregnant and of these women 71 (32.8%) of them suffered an adverse pregnancy outcome. By comparison, only 62 of 195 (31.8%) non Aboriginal women but nine out of 21 (41.9%) Australian Aboriginal women suffered from a previous adverse pregnancy outcome.

The clinical LGT GBS isolates found in this study of Brisbane women were typed and all nine GBS serotypes plus non typeable GBS serotypes were detected. Seventy women tested GBS culture positive and vaginal and/or perianal samples obtained from these women were evaluated. GBS serotype III was the serotype most frequently isolated from this total population, from 47.4% of pregnant women and 51.7% of non pregnant women. From some women only a single GBS serotype was isolated: in these women we found that GBS serotype III (50%) was the predominant isolate, followed by GBS serotype Ia isolated from 16.7% women. In addition 4.2% of women were colonised with GBS serotypes; Ib, II and V, whilst GBS serotypes IV and VII were isolated from 2.1% women. Non typeable GBS strains confirmed by latex agglutination tests accounted for 11.9% of all strains isolated from these Brisbane women.

This study identified multiple serovars in 15 clinical samples and found that 22 (31.4%) women were colonised with mixed GBS serotypes in samples collected from both vaginal and perianal regions. In five women the combination of serotypes III/Ia were identified and in other women combinations of serotypes III/II, III/IV, III/V, III/VIII, Ia/IV and Ib/NT were also detected. In two instances three serotype combinations were detected in samples from one woman and these included serotypes III/Ib/II and III/Ia/Ib. Isolates were also typed for women who were colonised in both vaginal and perianal regions and it was found that only 10 participants had identical isolates in both regions. GBS serotype III was the predominant serotype detected in women tested in this study and this is the serotype that has previously been associated with invasive infections in neonates.

GBS neonatal disease is a world wide economic, health and social burden affecting different ethnic groups and is preventable. Currently no vaccine technology is available for the prevention of GBS neonatal disease and the most effective EOGND preventative protocol would be to test for maternal GBS colonisation during labour, or screen women for GBS at &gt36 weeks' gestation and administer intrapartum antibiotic prophylaxis (IAP) to all women who tested positive for GBS. In this current study we utilised a rapid bsp PCR assay to detect LGT GBS colonisation in women of child bearing age. The PCR assay identified 62.5% of all vaginal and perianal positive culture GBS samples. The specificity of the PCR assay was 89% while the positive and negative predictive values were 56.8% and 91.1% respectively. This PCR assay using the current parameters is not an effective GBS detection assay but could be further optimised in the near future. This PCR assay could be an effective test in the future with the development of an alternative DNA extraction method to InstaGene (BioRad). However, this PCR assay if used in conjunction with the current culture method is able to detect a further 8.9% of women colonised with asymptomatic GBS.

Brisbane women aged between 26 to 35 years who are pregnant and who are attending public health care agencies are at greatest risk of being colonised with GBS. No disparity was identified when ethnicity or social standing were assessed.

The overall results of this study demonstrate that the LGT GBS prevalence rate in Brisbane women is 26.2% but this rate was higher at 30.5% for women attending a Brisbane sexual health clinic and for pregnant women attending the Mater Mothers' antenatal clinic.

GBS serovar III has been identified as the dominant serovar in our population group and this strain has been reported as the major cause of GBS disease in neonates and infants aged to three months. Disparity (11.1%) was reported when the incidence of adverse pregnancy outcomes amongst Aboriginal women was compared to non Aboriginal women. From the outcomes of this study it has been suggested that Queensland adopt a screening based GBS preventative protocol. It has also been suggested that an Australian wide GBS prevention strategy may further reduce the incidence of neonatal disease.

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ID Code: 16462
Item Type: QUT Thesis (Masters by Research)
Supervisor: Knox, Christine & Mathews, Sarah
Keywords: Group B Streptococcus, GBS neonatal disease, neonatal morbidity, neonatal mortality, serovar, PCR assay
Divisions: Past > QUT Faculties & Divisions > Faculty of Science and Technology
Past > Schools > School of Life Sciences
Department: Faculty of Science
Institution: Queensland University of Technology
Copyright Owner: Copyright Karen Leigh Taylor
Deposited On: 03 Dec 2008 04:03
Last Modified: 28 Oct 2011 19:48

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